Abstract

A major problem concerning the construction aad maintenance of marine
culture ponds at Mandapam has been that dykes are subject to easy erosion and
damage because of the incohesiveness and porosity of earth, which chiefly consists
of sand, fragments of corals and molluscan shells. Crests and slopes of dykes
are liable to be washed off easily in rains, and dyke bases are eroded by wave
action in the ponds. Experiments showed that dykes when built in a proportion
of 5-6 m basal width to 1 m height are capable of resisting these damages considerably.
To protect dykes' bases and to maintain their slopes, turfing is found
to be most effective and long lasting. Also, when a strip of the original ground
is left as it is all along the inner edges of ponds, the dykes tend to remain
free of damage. A grass belonging to the genus Chloris, which has shown a high
rate of propagation and a good earth-binding quality, is found to protect the
dykes well against the local climatic and soil conditions. It is also found that,
by allowing enough time for the dykes to season and consolidate and for the
pond bottom to become compact, seepage can be reduced by 75%. Further reduction
up to 96% is possible by covering the slopes and dyke bases with protective
linings made of locally available cheap materials. Structural work of a simple
culvert type sluice, successfully designed' and constructed for free flow of water
to the ponds, is explained.